1. Field of the Invention
The present invention relates to a screw shaft for such as an elevator, and more particularly to a screw type elevator having a second or auxiliary driving device for moving a screw shaft and/or a carriage and for allowing the carriage to be moved to a safe location when the main or primary driving device or power has become failure.
2. Description of the Prior Art
Typical elevator systems comprise a carriage for moving a payload such as personnel or cargo traversely along a vertically elongated structural environment, and a finite length framework along which the vertically movable carriage through a guidable yoke slidably traverses, and one or more upright rails for guiding the carriage to move up and down relative to the elongated structural environment.
For example, U.S. Pat. No. 3,381,541 to Thireau et. al. discloses one of the typical elevator systems or transmission devices comprising a carriage guided to move up and down along one or more upright rails, and a flexible band employed with the use of friction arising out of the contact of the band and a supporting or backing support.
U.S. Pat. No. 3,815,710 to Shrum discloses another typical elevator system comprising a sensing circuitry to protect an elevator car from striking a dislodged counterweight or other structure, and the elevator car is to be moved relative to a structure having a number of floors or landings and for being guided to move up and down in a vertical path with wire ropes.
In both the typical elevator systems, only one motor driving means or device is provided and coupled to the carriage or the elevator car via the wire ropes for pulling and moving the carriage or the elevator car up and down relative to the elongated structural environment.
However, when the electric power supply is cut off, particularly when earthquakes are occurred, or when the single motor driving means or device is damaged or become failure, the carriage or the elevator car may no longer be moved up and down relative to the elongated structural environment, and may only be energized or moved again when the electric power supply is recovered.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional driving mechanisms for elevator systems.